Composition for forming corrosion resistant composite coating

ABSTRACT

A saltwater corrosion resistant hybrid composite is provided. The saltwater corrosion resistant hybrid composite coating includes at least one conductive polymer, crumb rubber, and a cured epoxy. The conductive polymer is dispersed in particles of the crumb rubber to form a network. The network is dispersed in the cured epoxy to form the saltwater corrosion resistant hybrid composite coating. A method of making of the saltwater corrosion resistant hybrid composite is also provided. A metal when coated with the resistant hybrid composite of the present disclosure is resistant to salt-water corrosion.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.17/713,852, now allowed, having a filing date of Apr. 5, 2022.

BACKGROUND Technical Field

The present disclosure is directed to a corrosion resistant composite,and particularly to a saltwater corrosion resistant hybrid composite,and a method of preparing the saltwater corrosion resistant hybridcomposite.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentinvention.

Significant exposure to salt water can cause corrosion of metalsurfaces. Various corrosion inhibitors such as, alkyd-based coatings,oil-based coatings using natural oils, water emulsion-based coatings,urethane-based coatings, chlorinated rubber-based coatings, vinyl-basedcoatings, epoxy coatings, and zinc-based coatings, have been developedto inhibit corrosion. However, most of the conventionally used corrosionresistant coatings lack effective corrosion resistance when exposed tomarine and industrial environmental conditions. Further, highmanufacturing cost is a major drawback of such conventional coatings.Hence, there is a need for an efficient, long-lasting and an inexpensivecorrosion resistant coating which may substantially reduce or eliminatethe above limitations.

SUMMARY

In an exemplary embodiment, a saltwater corrosion resistant hybridcomposite coating is described. The saltwater corrosion resistant hybridcomposite coating includes at least one conductive polymer, crumb rubber(CR), and a cured epoxy. The conductive polymer is dispersed inparticles of the crumb rubber to form a network, wherein at least aportion of the crumb rubber is covalently bound to the conductivepolymer. The network is dispersed in the cured epoxy to form thesaltwater corrosion resistant hybrid composite coating.

In some embodiments, the network includes 1-10 wt. % of the crumb rubberand 90-99 wt. % of the conductive polymer, based on the total weight ofthe crumb rubber and the conductive polymer.

In some embodiments, the saltwater corrosion resistant hybrid compositecoating includes 1-10 wt. % of the conductive polymer and the crumbrubber and 90-99 wt. % of the cured epoxy based on the total weight ofthe conductive polymer, the crumb rubber, and the cured epoxy.

Some embodiments include one or more conductive polymers selected from agroup including a polyaniline (PANI), a polypyrrole (PPy), apolythiophene (PTh), a polyphenylene sulfide (PPS), a polyacetylene(PA), a polyphenylene vinylene (PPV), a poly(3,4-ethylenedioxythiophene)(PEDOT), a polycarbazole (PCz), a polyindole (PIn), a polyazepine, apolypyrene (PP), a polyazulene (PAz), and a polynaphthalene.

In some embodiments, the crumb rubber particles are heated to atemperature of 200 to 400 degrees Celsius (° C.) before the conductivepolymer is added to form the network.

In some embodiments, the crumb rubber particles are pre-treated with oneor more antifouling compounds selected from a group including copperoxide, zinc oxide, tributyltin, and dichlorooctylisothiazolinone(DCOIT).

In some embodiments, the crumb rubber particles are pre-treated with oneor more selected from a group including bleach, trichloroisocyanuricacid, N-chlorosuccinimide, N-bromosuccinimide, chloramine-T, Cl₂, andBr₂.

In some embodiments, the cured epoxy is a blend of at least one epoxyresin and at least one hardener. In some embodiments, the epoxy resin isat least one selected from a group including bisphenol A, and bisphenolF. In some embodiments, the hardener is at least one selected from agroup including phenols, aromatic amines, aliphatic amines, and thiols.The blend includes 80-95 wt. % epoxy resin and 5-20 wt. % hardener,based on the total weight of the epoxy resin and the hardener.

In some embodiments, the saltwater corrosion resistant hybrid compositecoating includes 5-10 wt. % polyurethane, based on the total weight ofthe polyurethane, crumb rubber, conductive polymer, and cured epoxy.

In some embodiments, the crumb rubber is a crumb rubber powder. Thecrumb rubber powder particles have an average size of 200 to 600micrometer (μm).

In some embodiments, a saltwater corrosion resistant surface is coatedwith the saltwater corrosion resistant hybrid composite coating. Thesaltwater corrosion resistant surface is at least partially coated witha layer of the saltwater corrosion resistant hybrid composite coating.The layer has a thickness of 40 to 100 μm.

In some embodiments, the surface is at least one material selected froma group including iron, steel, copper, aluminum, nickel, zinc, cobalt,lead, chromium, tantalum, titanium, zirconium, silver, and niobium.

In some embodiments, the layer is coated on the surface with anelectrospray deposition. The layer at least partially has a mushroompattern.

In some embodiments, the saltwater corrosion resistant surface includesa corrosion potential of −350 to −320 millivolt (mV) after at least 14days in a solution of 3-7% salt dissolved in water.

In some embodiments, the saltwater corrosion resistant surface includesan impedance modulus (|Z|) of 1×10⁸⁻⁹ ohm square centimeter (Ωcm²).

In another exemplary embodiment, a method of making a saltwatercorrosion resistant hybrid composite is described. The method includesmixing a conductive polymer monomer and crumb rubber in an acid to forma suspension. The method further includes adding an oxidizing agent intothe suspension and stirring for at least 10 hours at a temperaturegreater than 25° C. to form a reaction mixture. The method furtherincludes filtering and washing the reaction mixture with the acid andde-ionized water to form a wet powder. Furthermore, the method includesdrying the wet powder at a temperature greater than 75° C. for at least10 hours under vacuum to form a dry powder. The method further includessonicating the dry powder in an aprotic solvent for at least 30 minutesto form a dispersion. The method further includes mixing the dispersionwith a hardener and sonicating for at least 30 minutes to form a uniformdispersion. The method further includes evaporating the aprotic solventfrom the uniform dispersion to leave a hardener suspension. The methodfurther includes mixing the hardener suspension with an epoxy resin anddegassing at a temperature greater than 25° C. for at least 10 minutesto form a corrosion resistant hybrid composite.

In some embodiments, a method of inhibiting corrosion on a surface in asaltwater environment includes partially coating the surface with atleast one layer of the saltwater corrosion resistant hybrid compositecoating.

The foregoing general description of the illustrative present disclosureand the following detailed description thereof are merely exemplaryaspects of the teachings of this disclosure and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of this disclosure and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a schematic flow diagram of a method of forming a saltwatercorrosion resistant hybrid composite, according to certain embodiments;

FIG. 2 is an exemplary flow diagram of the method of forming thesaltwater corrosion resistant hybrid composite, according to certainembodiments;

FIG. 3 illustrates graphical representation of bode plots of coatedmetallic substrates, according to certain embodiments; and

FIG. 4 illustrates graphical representation of partial dependence plot(PDP) curves for the coated metallic substrates, according to certainembodiments.

DETAILED DESCRIPTION

In the drawings, like reference numerals designate identical orcorresponding parts throughout the several views. Further, as usedherein, the words “a,” “an” and the like generally carry a meaning of“one or more,” unless stated otherwise.

Furthermore, the terms “approximately,” “approximate,” “about,” andsimilar terms generally refer to ranges that include the identifiedvalue within a margin of 20%, 10%, or preferably 5%, and any valuesthere between.

Embodiments of the present disclosure are directed to a saltwatercorrosion resistant hybrid composite coating, otherwise referred to asthe ‘coating’. The coating can be applied to surfaces or substrates,such as steel, carbon steel, stainless steel and any other metallicsubstrate used or known in the art, that are susceptible to corrosion,particularly in marine environments. Experimental results with thecoating on the surfaces or substrates demonstrated a significantincrease in anti-corrosion behaviors. In addition, the coating exhibitslonger service life, enhanced biocompatibilities, and long-lastingantibacterial properties at low cost, thereby circumventing thedrawbacks such as high manufacturing cost, and low corrosion resistanceproperties of the prior art.

The saltwater corrosion resistant hybrid composite coating includes oneor more conductive polymers, crumb rubber (CR), and a cured epoxy. In anembodiment, the conductive polymer is dispersed in particles of the CRto form a network, and the network of conductive polymer and CRparticles is dispersed in the cured epoxy to form the saltwatercorrosion resistant hybrid composite coating. In an embodiment, at leasta portion of the crumb rubber particles are covalently bound to theconductive polymer. A conductive polymer, more precisely intrinsicallyconducting polymer, is a polymer which conducts an electrical currenttherethrough in one or more valence states of the polymer. Intrinsicelectrical properties make the conductive polymer a potential corrosioninhibiting composition. Some embodiments include one or more conductivepolymers selected from a group including a polyaniline (PANI), apolypyrrole (PPy), a polythiophene (PTh), a polyphenylene sulfide (PPS),a polyacetylene (PA), a polyphenylene vinylene (PPV), apoly(3,4-ethylenedioxythiophene) (PEDOT), a polycarbazole (PCz), apolyindole (PIn), a polyazepine, a polypyrene (PP), a polyazulene (PAz),and polynaphthalene. In some embodiments, the conductive polymer may bea poly(para-phenylene) (PPP), poly (3-alkyl-thiophenes) such as a poly(3-hexyl thiophene), a poly (3-methyl thiophene) and a poly-(3-octylthiophene), a polyisothianapthene, a poly-(3-thienylmethylacetate), apolyquinoline, apolyheteroarylenvinylene, in which a heteroarylene groupmay include, but is not limited to, a thiophene, a furan or a pyrrole, apoly-(3-thienylethylacetate), and derivatives, copolymers andcombinations thereof. In an embodiment, the conductive polymer is PANI.

In an embodiment, the CR is obtained from automotive and truck scraptires. In an embodiment, the crumb rubber particles are 1-6 mm,preferably 2-5, or 3-4 mm in size. In an embodiment, the CR is crumbrubber powder. The crumb rubber powder particles have an average size of200 to 600 μm, preferably 300-500, or 350-450 μm.

In an embodiment, the network of CR and conductive polymer includes 1-10wt. % of CR, preferably 3-8, or 4-5 wt. %, and 90-99 wt. % of conductivepolymer, preferably 92-97, or 95-96 wt. % based on the total weight ofthe conductive polymer, and the CR.

In an embodiment, the saltwater corrosion resistant hybrid compositecoating includes 1-10 wt. %, preferably 3-8, or 4-5 wt. % of theconductive polymer and the crumb rubber and 90-99 wt. %, preferably92-97, or 95-96 wt. % of the cured epoxy based on the total weight ofthe conductive polymer, the CR, and the cured epoxy.

In some embodiments, the cured epoxy is a blend of at least one epoxyresin and at least one hardener. In some embodiments, the blend includes80-95 wt. % epoxy resin, preferably 83-92, or 85-90 wt. %, and 5-20 wt.% hardener, preferably 8-17, or 10-15 wt. % based on the total weight ofthe epoxy resin and the hardener. The epoxy resin is at least oneselected from a group including bisphenol A, and bisphenol F and thehardener is one or more selected from a group including phenols,aromatic amines, aliphatic amines, and thiols.

In some embodiments, the coating may also include polyurethane, phenolicresins, alkyd resins, aminoplast resins, vinyl alkyds, silicone alkyds,uralkyds, urethane resins, unsaturated polyester resins, silicones,vinyl acetates, vinyl acrylics, acrylic resins, vinyl resins,polyimides, unsaturated olefin resins, fluorinated olefin resins, or acombination thereof. In an embodiment, the coating further includes 5-10wt. % polyurethane, preferably 6-9, or 7-8 wt. %, based on the totalweight of the polyurethane, crumb rubber, cured epoxy, and conductivepolymer.

In some embodiments, the CR particles are pre-treated with one or moreantifouling compounds selected from a group including the followingcopper oxide, zinc oxide, tributyltin, and dichlorooctylisothiazolinone(DCOIT). In some embodiments, the CR is soaked in a solution of at leastone antifouling compound for at least 1 hour, preferably 1-10 hours, or2-5 hours, before incorporation into the network of CR and conductivepolymer. In some embodiments, the antifouling compound prevents theattachment of organisms such as but not limited to, oysters andbarnacles, to the surface described later in the disclosure.

In some embodiments, the CR particles are heated to a temperature of 200to 400° C., preferably 250-350, or 300° C. before the conductive polymeris added to form the network. The heating of the CR allows forpenetration of the conductive polymer into the particles, therebyimproving contact surface area.

In some embodiments, the surface of the CR particles is functionalizedwith at least one halogen before their incorporation into the saltwatercorrosion resistant hybrid composite coating. In some embodiments, thehalogen may be chloride, bromine, and/or iodine. In an embodiment, therubber is functionalized with a halogen by submerging the rubber in asolution of a halogenation agent for at least 1 minute. In someembodiments, the halogenation agent is at least one selected from thegroup consisting of bleach, trichloroisocyanuric acid,N-chlorosuccinimide, N-bromosuccinimide, chloramine-T, Cl₂ and Br₂. Inan embodiment, the halogen substituted crumb rubber is further modifiedto form a Grignard reagent and reacted with carbon dioxide, asubstituted nitrile, a substituted carbonyl, and/or a substitutedepoxide, to form a carboxylic acid, a carbonyl, a secondary or tertiaryalcohol, and/or a primary alcohol, respectively, under reactionconditions known in the art. In an embodiment, the carboxylic acidfunctionalized crumb rubber may be further modified with thionylchloride, and/or an amine to form an acylchloride, and/or an amide,respectively, under reaction conditions known in the art.

In an embodiment, following functionalization of the crumb rubbersurface, the functionalized crumb rubber is combined with a monomer ofthe conductive polymer. In some embodiments, a portion of the monomerreacts with the functionalized crumb rubber surface, resulting incovalent bonding between the crumb rubber and the conductive polymer. Insome embodiments, a portion of the monomer polymerizes resulting in apolymer that connects the crumb rubber particles through covalentbonding of the polymer to the surface of the crumb rubber and throughthe polymer chain to an adjacent crumb rubber particle, creating anetwork. In an embodiment, the monomer has two or three polymerizationsites. In an embodiment, the monomer is p-phenylenediamine. In anembodiment, the conductive polymer is polyaniline, and a crosslinkingagent is added to link units of the polyaniline, thereby creating anetwork of the covalently bound crumb rubber particles and conductivepolymer. In some embodiments, the crosslinking agent is glyceroldiglycidyl ether.

The cured epoxy acts as a binding agent. Hereinafter, the binding agentsrefer to materials which convert to adherent membranes on a metalsurface and may provide a non-thermoplastic matrix for the conductingpolymer blended therein. The binding agent makes the coating capable ofbeing directly applied to a metal surface.

The present disclosure also provides a surface coated with a layer ofthe saltwater corrosion resistant hybrid composite coating. The surfaceis one or more materials selected from a group including iron, steel,copper, aluminum, nickel, zinc, cobalt, lead, chromium, tantalum,titanium, zirconium, silver, and niobium. In some embodiments, thesurface is partially, 80%, or 90%, or completely coated with a layer ofthe saltwater corrosion resistant hybrid composite coating. Thecorrosion protection may even be provided by components of the coatingin the presence of gaps in the coating on the surface. In an embodiment,the coating may be applied over exposed surfaces of metal substrates. Inan alternate embodiment, the coating may be applied as an interlayerbetween a pair of exposed metal surfaces. The layer has a thickness of10-1000 μm, preferably 40-500 μm, 50-200, or 70-100 μm. In someembodiments, the layer is coated on the surface with electrospraydeposition. In some embodiments, the layer is coated on the surface byvarious methods including, but not limited to, coater, spray coater orpainting by using a brush. In an embodiment, the layer partially orcompletely has a mushroom pattern. In some embodiments, the mushroompattern is microstructures approximately 1-500 μm in size. In someembodiments, the mushroom pattern prevents the attachment of organismssuch as but not limited to, oysters and barnacles, to the surface.

In an embodiment, the surface includes a corrosion potential of −350 to−320 mV, preferably −350 to −330, or −350 to −340 mV after at least 14days in a solution of 3-7% salt dissolved in water. This corrosionpotential is improved over surfaces coated with only cured epoxy, orsurfaces with no coating.

In an embodiment, the surface also includes an impedance modulus (|Z|)of 1×10⁸⁻⁹ Ω cm², preferably 1×10^(8.5) Ω cm2, or 1×10⁹ Ω cm². Theimpedance modulus is improved at least 1000 times over surfaces coatedonly with cured epoxy, or surfaces with no coating.

Referring to FIG. 1 , a schematic flow diagram of a method 100 of makinga saltwater corrosion resistant hybrid composite is illustrated. Theorder in which the method 100 is described is not intended to beconstrued as a limitation, and any number of the described method stepscan be combined in any order to implement the method 100. Additionally,individual steps may be removed or skipped from the method 100 withoutdeparting from the spirit and scope of the present disclosure.

At step 102, the method 100 includes mixing a conductive polymer monomerand crumb rubber in an acid to form a suspension. In some embodiments,the acid has a concentration of 1 to 5 Molar (M), preferably 1-3 M, or1-2 M. In some embodiments, the acid can be hydrochloric acid,hydrobromic acid, nitric acid, or sulfuric acid. In an embodiment, theacid is hydrochloric acid. In an embodiment, the HCl has a concentrationof 2M.

At step 104, the method 100 includes adding an oxidizing agent into thesuspension and stirring for more than 10 hours, preferably 10-20 hours,or 14-16 hours, at a temperature greater than 25° C., preferable 25-50°C. or 30-40° C. to form a reaction mixture. In some embodiments, theoxidizing agent may include, but is not limited to, ceric ammoniumnitrate, ceric sulfate, potassium nitrate, peroxymonosulfuric acid, orany combination thereof. In an embodiment, the oxidizing agent isammonium persulfate (APS).

At step 106, the method 100 includes filtering and washing the reactionmixture with acid and de-ionized water to form a wet powder. In someembodiments, the acid is the same as step 102.

At step 108, the method 100 includes drying the wet powder at atemperature greater than 75° C., preferably 75-100, or 80-90° C. formore than 10 hours, preferably 10-24 hours, or 15-20 hours under vacuumto form a dry powder.

At step 110, the method 100 includes sonicating the dry powder in anaprotic solvent for more than 30 minutes, preferably 30-60 minutes, or40-50 minutes, to form a dispersion. In some embodiments, the aproticsolvent can be benzene, carbon tetrachloride, carbon disulfide, or anycombination thereof. In an embodiment, the aprotic solvent is acetone.

At step 112, the method 100 includes mixing the dispersion with ahardener and sonicating for at least 30 minutes, preferably 30-60minutes, or 40-50 minutes, to form a uniform dispersion. In anembodiment, the hardener is polyamine.

At step 114, the method 100 includes evaporating the aprotic solventfrom the uniform dispersion to leave a hardener suspension. In someembodiments, the evaporating is through heating, or under nitrogen flow.

At step 116, the method 100 includes mixing the hardener suspension withan epoxy resin, followed by de-gassing at a temperature greater than 25°C., preferably 25-40, or 30-35° C. for more than 10 minutes, preferably10-30 minutes, or 20-25 minutes to form a corrosion resistant hybridcomposite.

The present disclosure also provides a method of inhibiting corrosion ona surface in a saltwater environment using saltwater corrosion resistanthybrid composite coating. The method includes partial or completecoating of one or more layers of the saltwater corrosion resistanthybrid composite coating onto the surface.

EXAMPLES

The following examples describe and demonstrate exemplary embodiments ofthe coating as described herein. The examples are provided solely forthe purpose of illustration and are not to be construed as limitationsof the present disclosure, as many variations thereof are possiblewithout departing from the spirit and scope of the present disclosure.

Example: Materials Required

Aniline, hydrochloric acid (HCl), ammonium persulfate (APS), polyaminehardener, acetone, NaCl solution, water, crumb rubber powder, and epoxyresin.

Example: Method of Preparation

Referring to FIG. 2 , an exemplary flow diagram of the method 100 offorming the saltwater corrosion resistant hybrid composite isillustrated. 5 milliliter (ml) polyaniline (PANI) was dropped into 70 mlof 2 M of HCl containing various amounts of a CR powder (such as 1%, 5%and 10%) under ultrasonic stirring to make a uniform suspension. After12 hours (hrs.), 5 grams (g) of APS was dissolved in 20 ml de-ionizedwater and was dropped into the uniform suspension with constant stirringfor about 1 hr. Polymerization was allowed to proceed for 12 h at 30° C.to form a reaction mixture. Further, the reaction mixture was filtered,and washed with 2 M HCl and de-ionized water and was subsequently driedat 90° C. for 12 h in vacuum to obtain a tint blackish green powder.

A cured epoxy including a mixture of epoxy resin and a hardener with aratio of 3:1, was utilized to prepare epoxy coatings. Various amounts ofprepared PANI/CR composites (1, 5 and 10 wt. %) were dispersed in anacetone solvent using ultrasonication for 1 h. Subsequently, a resultantdispersion was ultrasonicated with a polyamine hardener for 30 minutes,to get a uniform dispersion. The acetone solvent was evaporated byheating at 50° C. with stirring. Further, a portion of the epoxy resinwas mixed with the prepared dispersion followed by degassing in an ovenfor 15 minutes to obtain a corrosion resistant hybrid composite. Thecorrosion resistant hybrid composite was coated on metallic substratesby a drawdown bar coater. Further, wet coated metallic substrates wereallowed to dry at room temperature.

The developed coating has an average thickness of 60 μm. The corrosionresistant performance of coated specimen was evaluated in 3.5% NaClsolution using the potentiodynamic polarization and electrochemicalimpedance spectroscopic (EIS) measurements. Electrochemical corrosiontest results confirmed that corrosion protection performance of theepoxy coatings has improved with the addition of PANI/CR composite up to10 wt. %, in comparison to the performance of epoxy coatings known inthe art as well as uncoated substrate.

Referring to FIG. 3 , a graphical representation of bode plots of thecoated metallic substrates in 3.5% NaCl solution is illustrated. Thecoated metallic substrates exhibited a two-time constant behavior in afrequency range of 10⁻² to 10⁵ Hz. A time constant found at a highfrequency region is connected to responses of the NaCl solution/coatinginterface. However, a time constant at a low frequency region isassociated to a corrosion phenomenon occurring at the NaClsolution/metallic substrate interface. Generally, a value of animpedance modulus (|Z|) is inversely proportional to corrosion rate. Theimpedance modulus (|Z|) of the metallic substrates with pure epoxycoatings was found to be around 10⁵ to 10⁶, however, epoxy coatings withPANI/CR composites exhibited Z about 10⁹, which reveals distinctivenessof intact, well adherent composite coatings on the metallic substrates.

Further, Z at 1 Hz replicates the total corrosion protection offered bythe epoxy composite coatings, which is observed to increase in the orderof pure epoxy, epoxy/CR, epoxy/PANI/CR displaying an improved impedancein comparison with a bare substrate. Moreover, epoxy coatings processedwith an addition of 10 wt. % PANI/CR have exhibited higher corrosionprotection performance on the metallic substrates in 3.5% NaCl solution.

FIG. 4 refers to a graphical representation of partial dependence plot(PDP) curves for coated metallic substrates after an immersion of 14days in 3.5% NaCl solution. Anodic sites are attributed to a corrosionprocess of the coated metallic substrates, while the cathodic sites areaccompanied with evolution of hydrogen. A less corrosion current density(i_(corr)) and a noble corrosion potential (E_(corr)) representedenhancement in a surface protection against corrosion. From the FIG. 4 ,it can be observed that the current densities of the epoxy coatings withthe inclusion of the CR decrease by one order of magnitude, incomparison to pure epoxy substrates. The epoxy/PANI/CR coating was foundto have the highest surface protective performance with an E_(corr), of−335 mV and at a lower cathodic current density with respect to othercoated metallic substrates, thereby suggesting an increased corrosionprotection behavior of epoxy coatings after the addition of PANI/CR.

The coating of the present disclosure finds application in variousindustries for protecting metallic substrates such as steel structuresin marine environments. The coating may also be used in industries andapplications including, but is not limited to, automobile, aircraft andshipping industry as a surface coating; bridge and road constructionindustry as a coating for exposed steel on bridges; constructionindustry as a coating for structural steel; chemical and industrialmanufacturers as a coating for chambers, vessels, metallic machines; themedical industry as a protective coating for metal leads inelectrocardiographs; in metallized textile industry and paintmanufacturing industries.

Cheap and easy availability of chemicals such as hydrochloric acid,aniline, or pyrrole, or ethylenedioxythiophene (EDOT), APS, epoxy resinresults in development of a cost-effective coating. Furthermore,inclusion of the crumb rubber from the automotive and truck scrap tiresalso enables recycling of the crumb rubber. Presence of epoxy/PANI/CRmay enhance the lifetime of a coated structure due to enhanced corrosionprotection. The coating of the metal surfaces or substrates with thecoating of the present disclosure imparts reduced corrosion rate,enhanced biocompatibilities, and antibacterial performance, and longerservice life compared to commercial epoxy coatings. The coating in thepresent invention is easy to apply and involves a simple fabricationprocess.

Obviously, numerous modifications and variations of the presentdisclosure are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

The invention claimed is:
 1. A curable composition for forming acorrosion resistant composite coating, comprising, in the form of auniform dispersion: at least one aprotic solvent; at least oneconductive polymer; crumb rubber; and a curable epoxy component; whereinthe conductive polymer and the crumb rubber are present as a powderedcomposite material comprising the conductive polymer mixed withparticles of the crumb rubber to form a network; and wherein at least aportion of the crumb rubber is covalently bound to the conductivepolymer in the network.
 2. The curable composition of claim 1, whereinthe network comprises: 1-10 wt. % of the crumb rubber; and 90-99 wt. %of the conductive polymer, based on the total weight of the crumb rubberand the conductive polymer.
 3. The curable composition of claim 1,comprising: 1-10 wt. % of the conductive polymer and the crumb rubber;and 90-99 wt. % of the curable epoxy component based on the total weightof the conductive polymer, the crumb rubber, and the curable epoxycomponent.
 4. The curable composition of claim 1, wherein: theconductive polymer is at least one selected from a group consisting of apolyaniline (PAM), a polypyrrole (PPy), a polythiophene (PTh), apolyphenylene sulfide (PPS), a polyacetylene (PA), a polyphenylenevinylene (PPV), a poly(3,4-ethylenedioxythiophene) (PEDOT), apolycarbazole (PCz), a polyindole (PIn), a polyazepine, a polypyrene(PP), a polyazulene (PAz), and a polynaphthalene.
 5. The curablecomposition of claim 1, wherein: the crumb rubber is heated to atemperature of 200 to 400 degree Celsius (° C.) before the conductivepolymer is added to form the network.
 6. The curable composition ofclaim 1, wherein: the crumb rubber is pretreated with at least oneantifouling compound selected from a group consisting of the followingcopper oxide, zinc oxide, tributyltin, and dichlorooctylisothiazolinone(DCOIT).
 7. The curable composition of claim 1, wherein: the crumbrubber is pretreated with at least one selected from a group consistingof bleach, trichloroisocyanuric acid, N-chlorosuccinimide,N-bromosuccinimide, chloramine-T, Cl₂ and Br₂.
 8. The curablecomposition of claim 1, wherein: the curable epoxy component comprises80-95 wt. % of an epoxy resin and 5-20 wt. % of a hardener, based on thetotal weight of the epoxy resin and the hardener.
 9. The curablecomposition of claim 8, wherein: the epoxy resin is bisphenol A.
 10. Thecurable composition of claim 8, wherein: the hardener is at least oneselected from a group consisting of phenols, aromatic amines, aliphaticamines, and thiols.
 11. The curable composition of claim 1, furthercomprising: 5-10 wt. % polyurethane, based on the total weight of thepolyurethane, the crumb rubber, the curable epoxy component, and theconductive polymer.
 12. The curable composition of claim 1, wherein: thecrumb rubber is a crumb rubber powder; wherein the crumb rubber powderparticles have an average size of 200 to 600 micrometer (μm).
 13. Amethod of inhibiting corrosion on a surface in a saltwater environment,comprising: at least partially coating at least one layer of the curablecomposition of claim 1 onto the surface.